Scientific discovery often happens by accident, i.e. unpredictably. And when you're not expecting to discover something, you're obviously not being precise about it.

A concrete example is the accidental discovery of the cosmic microwave background radiation. If you Google "accidental discovery" you'll find hundreds of other examples.

Or, if you prefer an Asimov quote:

"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but 'That's funny...'"